Proportional blower

ABSTRACT

A proportional blower having two inlets and a single outlet, and a pair of damper plates mounted for simultaneous movement one toward and the other away from such inlets for respectively decreasing and increasing the effective cross-sectional areas of such inlets in inverse amounts. Also associated with one of the blower inlets is a fixed or variable restriction which aids in maintaining a substantially constant discharge from the blower outlet during modulation of one or both of the blower inlets.

United States Pat ent 1 13,625,629

[72] Inventors gllilollnp fini tz [56] References Cited a er e g Hunter Morrison, Jr., Pepper Pike; George UNITED STATES PATENTS pp, Chagrin Falls, all of 01110 1,085,045 1 1914 Holzapfel 415 157 [2 App 43 318 2,143,100 1/1939 Anderson." 415/165 [22] Filed Jmle 4,1970 2,874,642 2/1959 Forrest 415/157 [45] Patented 7, 1971 i 3,440,946 4/1969 Morrison 98/38 [73] Assignee M K M Corporation Primary Examiner-Henry F. Raduazo Chagrin Falls, Ohi Attorney-Oberlin, Maky, Donnelly & Renner ABSTRACT: A proportional blower having two inlets and a single outlet, and a pair of damper plates mounted for simultaneous movement one toward and the other away from such [54] PROPORTIONAL BLOWER 10 Claims, 13 Drawing Figs.

[52] U.S. Cl ..l 415/157, inlets for respectively decreasing and increasing the effective 98/38 cross-sectional areas of such inlets in inverse amounts. Also '[5 1] Int. Cl. ..F0ld 17/14, associated with one of the blower inlets is a fixed or variable F24f 7/00 restriction which aids in maintaining a substantially constant [50] Field of Search 415/ I57, discharge from the blower outlet during modulation of one or 158, 165; 98/38 both of the blower inlets.

PATENTEDUEB 7197: 3.625629 SHEET 1 OF 3 INVENTORS THOMPSON MORRISON HUNTER MORRISON, JR. GEORGE F. KNAPP PATENTEDDEB Han I 3.625629 SHEET 2 0F 3 3 I 5.: 5 J INVENTORS.

THOMPSON MGR/W501! HUNTER MORRISON, JR. GEORGE E KNAPP ATTORNEYS PATENTEDDEC mn 3,6251629 SHEET 3 [IF 3 l2 l6 5:" ..Z.5

INVENTORS.

r'noMkso/v MORRISON HUNTER MORRISON, JR. GEORGE E K/VAPP ATTORNEYS PROPORTIONAL BLOWER BACKGROUND OF THE INVENTION This invention relates generally as indicated to a proportional blower, and more particularly, to certain improvements in proportional blowers generally of the type shown and described in U.S. Pat. No. 3,440,946, granted to Thompson Morrison on Apr. 29, I969.

In such aforementioned US. Pat. No. 3,440,946, which is incorporated herein by way of reference, there is shown an open centrifugal flower having a pair of spaced inlets isolated from each other for communication with different sources of gases, and a single outlet through which the gases from both sources are discharged after being admixed within the blower.

Variations in the composition of the discharge mixture from the blower of the aforementioned patent may be obtained while maintaining the rate of discharge substantially constant by providing the blower with a movable damper adjacent each inlet and drive means for moving one of the dampers along a path which reduces the effective cross-sectional area of its corresponding inlet port, and simultaneously moving the other damper along a path which increases the effective cross-sectional area of its corresponding inlet port so that the equivalent orifice of the blower is held substantially constant throughout the movement of both dampers.

One of the main advantages of such a blower is that it is capable of mixing air or other gases from separate sources in varying volumetric ratios to meet certain supply requirements such as temperature and humidity while still maintaining substantially constant the total volume of air circulated by the blower. In ventilating systems, such a blower arrangement may be advantageously used to mix specified amounts of outside or conditioned air with recirculated air for proper ventilation of the building. Moreover, by modulating the amount of outside or conditioned air anywhere from the minimum required for proper ventilation up to 100 percent outside or conditioned air, maximum advantage may be taken of the outside air in the one case or conditioned air in the other case to obtain natural cooling, heating and humidifying of a building, depending of course on the relative temperature and humidity of the inside and outside air and the temperature and humidity desired.

However, some difficulty has been encountered in determining the proper spacing between the damper plates to maintain a substantially constant or uniform air delivery for all positions of the damper plates. I-Ieretofore, it was the usual practice to detennine such spacing by moving one of the damper plates to the full closed position and moving the other damper plate to the full open position, which was taken as the blower rating for maximum or 100 percent flow capacity for the blower. Theoretically, if both damper plates were the moved to an intennediate position half way between the full open position for one of the damper plates, the combined flow through both of the inlet ports would be such I percent flow capacity. In actual practice, however, it has been found that the total flow through both inlet ports with the damper plates in such half open position is somewhat greater than the desired 100 percent flow, and such flow also varies somewhat from the desired maximum or 100 percent position during modulation of the flow through simultaneous movement of both damper plates.

SUMMARY OF THE INVENTION With the foregoing in mind, it is a principal object of this invention to provide a proportional blower of the type generally described above, but which maintains a more constant rate of discharge from the blower during modulation of one or both inlets as required to meet certain supply conditions.

Another object is to provide such a blower in which the desired rate of discharge therefrom may also be obtained at the 100 percent flow position for at least one of the inlets to the blower.

These and other objects of the present invention may be achieved by restricting one of the inlets to the blower in a fixed or variable manner so that the maximum discharge from the flower remains substantially constant even though the flow through the inlets is modulated from one source to the other. When a fixed restriction is provided at one of the inlets, the blower discharge will remain constant at the percent position for the other blower inlet, but as the damper plates are moved toward the 100 percent position for the restricted inlet, the total flow through the blower diminishes. However, where a variable restriction is provided, the discharge from the blower may be maintained substantially constant for all positions of the damper plates. Such a variable restriction may be in for form of a supplemental damper plate or plunger mounted for pivotal or axial movement with one of the damper plates for varying the size of one of the inlets to the blower or plenum chamber associated therewith as required to obtain the desired constant discharge through the blower outlet for all positions of the damper plates.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features herein after fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of a few of the various ways in which the principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS In the annexed drawings:

FIG. 1 is a schematic top plan view of a preferred form of blower constructed in accordance with this invention as seen with the upper wall of the surrounding housing removed and showing the damper plate for one of the blower inlets fully closed and the other damper plate fully open;

FIG. 2 is a schematic fragmentary end elevation view of the blower of FIG. I, as seen from the plane of the line 2-2;

FIG. 3 is a schematic partial longitudinal section through the blower of FIG. 2, taken on the plane of the line 3-3 thereof;

FIG. 4 is a schematic partial longitudinal section similar to FIG. 3 but showing both damper plates in their intermediate or half open positions, with a restrictor plate partially restricting the flow through the other inlet;

FIG. 5 is a schematic partial longitudinal section similar to FIG. 3, but showing the one damper plate fully closed and the other damper plate fully open with the restrictor plate pivoted outwardly so as not to restrict or obstruct flow through the associated inlet;

FIGS. 6, 8 and 9 are schematic partial longitudinal sections through a modified form of blower constructed in accordance with this invention in which an axially movable restrictor plunger has been substituted for the pivotal restrictor plate of FIGS. 1-5, such figures illustrating the various positions of the inlet damper plates and restrictor plunger corresponding to FIGS. 3, 4, and 5, respectively;

FIG. 7 is a schematic partial end elevation view of the blower of FIG. 6 as seen from the plane of the line 7-7 thereof;

FIGS. 10 through 12 are schematic top plan views of still another form of blower in accordance with this invention as seen with the upper wall of the surrounding housing removed and showing the various operating positions for the damper plates and restrictor plate; and

FIG. 13 is a schematic partial horizontal section through yet another form of blower constructed in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in detail to the drawing and first especially to FIGS. 1 through 5, there is shown a preferred form of proportional blower l in accordance with this invention including a rotor or blower wheel 2 mounted for rotation within a double inlet housing 3. The rotor 2 is supported by a central shaft 4 joumaled in bearing mounts 5 exteriorly of the blower housing 3. Rotation of the rotor 2 may be achieved by an electric motor 6 connected to the shaft 4 by means of a belt 7 and pulley 8 arrangement.

The blower housing 3 is contained within an external cabinet or main housing 9 which has a partition 10 therein dividing the main housing 9 into two separate plenum chambers 11 and 12 communicating with the respective blower inlets l3 and 14 and isolating such blower inlets from each other. Each plenum chamber 11 and 12 has an opening 15 and 16 therein to which separate ducts (not shown) may be connected for communicating such plenum chambers with separate sources of gases. During operation of the blower l, the gases are drawn into the interior of the blower housing 3 through the blower inlets l3 and 14 where they are admixed and subsequently discharged from the blower housing through an outlet 17 communicating with an opening 18 in the main housing 9.

Adjacent each of the blower inlets 13 and 14 are damper plates 19 and 20 which may be supported on the rotor shaft 4 by suitable bearings 21 for axial sliding movement of the damper plates toward and away from the respective blower inlets. Preferably, the damper plates 19 and 20 are connected together by a yokelike member 22 which straddles the rotor housing 3 and pennits simultaneous movement of the damper plates during movement of the yoke member. As apparent, such simultaneous movement of the damper plates 19 and 20 in either direction will inversely vary the relative effective areas of the blower inlets l3 and 14 thus to vary the relative amounts of gases entering the blower housing 3 from the plenum chambers 11 and 12. Thus, for example, movement of the yoke member 22 toward the right as seen in FIGS. 3-5, causes the damper plate 19 to move along a path which increases the effective cross-sectional area of its corresponding inlet 13, and simultaneously causes the other damper plate 20 to move along a path which decreases the effective cross-sectional area of its corresponding inlet 14. Movement of the yoke member 22 in the opposite direction has the reverse effect. By placing a sensing device 23in the blower outlet 17 to control the position of the damper plates 19 and 20 in response to such conditions as dry bulb, wet bulb, humidity, dew point, pressure or other index, gases of different compositions or temperatures may be mixed in various volumetric ratios to assure a minimum quantity of air, heat, latent moisture or other matter to be delivered from one source or the other a predetermined by the design.

If the relative spacing between the damper plates 19 and 20 in relation to the axial length of the rotor housing 3 is accurately determined, a substantially constant or uniform air delivery will also be obtained from the blower for all positions of the damper plates, which may be essential for proper ventilation of buildings and other uses. l-leretofore, it has been the usual practice to determine such spacing by moving one of the damper plates to the full closed position and moving the other damper plate to the full open position which is the desired 100 percent discharge capacity of the blower. Theoretically, if both damper plates are then moved to an intermediate position halfway between the full open position of one of the damper plates, the combined flow through both of the blower inlets will be the same as when only one of the blower inlets is fully open and the other is closed. However, in actual practice the total flow through both inlet ports with the damper plates in the half open position is somewhat greater than the desired 100 percent flow, and the total flow through the blower also varies somewhat during modulation of the blower inlets by movement of the damper plates in either direction.

In order to obtain such desired 100 percent flow through the blower of the present invention for all positions of the damper plates, the damper plates 19 and 20 are initially located at an intermediate position halfway between the full open position of one of the damper plates as before, but in addition a restrictor is provided for reducing the flow through one of the blower inlets. In the FIGS. 1 through 5 embodiment, such restrictor consists of a restrictor plate 25 hinged at 26 to one end of the blower housing 3 above one of the blower inlets 14 so that it hangs downwardly in overlying relation to a portion of the blower inlet. The restrictor plate 25 may be of any desirable shape and while it is shown covering approximately three-fourths of the blower inlet 14 when in the fully closed position, it will be appreciated that the size of the restrictor plate may be varied to obtain the amount of restriction desired. A slot 27 is provided in the lower edge of the restrictor plate 25 to permit pivotal movement of the restrictor plate without interference with the blower shaft 4 in a manner to be subsequently described.

The restrictor plate 25 is connected to the adjacent damper plate 20 as by means of a chain or rod 28 or suitable flexible linkage extending through aligned openings in the plates. The rod 28 is freely slidable within such openings and has enlarged ends for limiting relative sliding movement between the rod and plates. By proper selection of the length of the rod 28, the restrictor plate 25 will remain in its maximum restricting position during movement of the damper plates 19 and 20 from the FIG. 3 position in which the damper plate 19 for the unrestricted inlet 13 is fully open and the other damper plate 20 for the restricted inlet 14 is fully closed to the FIG. 4 position in which both of the damper plates are in their intermediate or half open positions to maintain a substantially constant or uniform discharge from the blower. Continued axial movement of the damper plates 19 and 20 from the FIG. 4 position to the FIG. 5 position causes outward swinging movement of the restrictor plate 25 because of its rod connection with the adjacent damper plate 20 to increase the flow area through the blower inlet 14 as the flow area of the blower inlet 13 decreases to still maintain a substantially constant discharge from the blower. The opening 29 in the restrictor plate 25 is slotted to permit the connecting rod 28 to pivot with the restrictor plate. When damper plate 19 is fully closed and the damper plate 20 is fully open as shown in FIG. 5, the restrictor plate 25 is pivoted outwardly sufficiently far so as not to obstruct the flow through the blower inlet 14, whereby the total discharge from the blower still remains constant at the percent flow position for the blower inlet 14.

In FIGS. 6 through 9 there is shown a modified form of proportional blower 30 which is generally similar to the blower 1 of the FIGS. 1 through 5 embodiment and accordingly the same reference numerals followed by a prime symbol are used to designate like parts. There is a difference, however, in the construction of the restrictor for one of the blower inlets 14. Instead of providing a hinged restrictor, a restrictor plunger 31 is mounted directly to the adjacent damper plate 20 for axial movement therewith. As best seen in FIG. 7, the restrictor plunger 31 is in the shape of a three-quarter cylinder having a slot 32 in the bottom surface thereof for accommodating the rotor shaft 4. There is also a guide 33 attached to the adjacent end of the blower housing 3 having an opening 34 therein corresponding to the cylindrical shape of the restrictor plunger 31 to provide a seal with the restrictor plunger when received within the blower inlet 14'.

During movement of the damper plates 19' and 20' from the FIG. 6 100 percent full open position for the damper plate 19 to the FIG. 8 half open position for both damper plates, the restrictor plunger 31 moves outwardly with its associated damper plate 20'. However, due to the axial overlap between the restrictor plunger 31 and guide member 33, the restrictor plunger 31 still restricts the flow through its associated blower inlet 14 to maintain a substantially constant discharge from the blower 30 during such initial movement of the damper plates to the FIG. 8 intermediate position.

Continued movement of the damper plates 19' and 20' from the FIG. 8 position to the FIG. 9 position causes disengagement of the restrictor plunger 31 from the guide 33 to provide for progressively increased flow through the associated blower inlet 14 as the flow through the other blower inlet 13' decreases, thereby still maintaining a substantially constant discharge from the blower. As before, when the damper plate associated with the restricted inlet 14 reaches the fully open position and the damper plate 19' associated with the other inlet 13' is fully closed, the restrictor plunger 31 is no longer effective so that a substantially constant discharge from the blower will still be maintained.

Referring nest to FIGS. 10 through 11, there is shown another form of blower 35 in accordance with this invention which is also quite similar to the blower 1 of the FIGS. 1 through 5 embodiment, and accordingly the same reference numerals followed by a prime symbol are used to designate like parts. Such blower also includes a restrictor plate 36 which is generally similar to the restrictor plate of the FIGS. 1 through 5 embodiment. However, the restrictor plate 36, rather than being hinged to the blower housing in overlying relation with one of the blower inlets, is hinged to the main housing 9 and extends part way across the opening 16' to the associated plenum chamber 12. Between the restrictor plate 36 and adjacent damper plate 20 there is a linkage connection 37 of suitable type for effecting pivotal movement of the restrictor plate 36 during axial movement of the damper plate 20.

With the damper plate 20' fully closed and the damper plate 19' fully open as shown in FIG. 10, all of the flow is through the blower inlet 13', and the restrictor plate 36 is in its initial maximum restricting position. However, during movement of the damper plates 19' and 20 to the intermediate position shown in FIG. 11, the restrictor plate 36 is pivoted to a slight extent as shown for restricting the flow into the plenum chamber 12' so that the total discharge from the blower remains substantially constant. Continued movement of the damper plates 19' and 20' from the FIG. 11 position to the FIG. 12 position causes further pivotal movement of the restrictor plate 36 for increased flow into the plenum chamber 12' to continue to maintain a substantially constant discharge from the blower. When the damper plate 20 reaches its full open position, the restrictor plate 36 no longer restricts flow into the plenum chamber 12' whereby a constant discharge from the blower is still obtained. Of course, in each instance, experimentation will be required to determine the proper size of the restrictor plate and length of linkage to obtain the same discharge from the blower for all positions of the damper plates.

While it is preferred that the restriction to one of the blower inlets be variable in a controlled manner as previously described, it will be apparent that a fixed restriction 40 may be also be provided to one of the blower inlets 14 as illustrated in the FIG. 13 blower embodiment to achieve the desired I00 percent flow through the blower 41 during movement of the damper plates 19' and 20' between the full open position of the blower inlet 13' and the intermediate open position for both the blower inlets 13' and 14'. However, with such a construction, the total discharge through the blower 41 will diminish as modulation occurs toward full open position for the restricted blower inlet 14'.

Adjustment of the position of the damper plates of the various blower embodiments disclosed herein may be accomplished in any convenient manner, as by providing a suitable reversible drive mechanism 42 within the main housing 9. Operation of the damper plate drive mechanism 42 may be controlled by the sensor 23 for delivery by the blower of a mix to suit the requirements controlled by the sensor.

When the blower is used for ventilation of a commercial building such as an office building or school, the plenum chamber 12 associated with the restricted blower inlet 14 is preferably connected by suitable duets with the air to be recirculated and the other plenum chamber 11 is connected to the outside air. During operation of the blower, the outside air is mixed with the room air to deliver a constant volume of air which may be discharged at a constant temperature or varia' ble temperature, depending upon the setting of the sensor 23.

If the sensor is set for discharge of a fixed temperature air supply and the temperature of the outside air is less than that of the recirculated air, a drop in temperature of the supply air from the blower below the setting of the sensor will cause the damper plates to move in a direction closing the outside air inlet 13 and opening the recirculated air inlet 14. Conversely, if the supply temperature tends to go above the setting of the sensor, the dampers will be caused to move in a direction opening the outside air inlet 13 and closing the recirculating air inlet 14.

If, however, the sensor 23 is placed in a position remote from the blower discharge and is set to the desired room temperature, the position of the damper plates will be varied to supply different air temperatures to obtain maximum natural cooling and heating of the room. When the room temperature drops below the desired temperature, the damper plates will be caused to move in a direction closing the outside air inlet. A stop 42 shown schematically in FIG. 13 may be provided on the damper 19 associated with the outside air inlet 13' to prevent complete closing so that a minimum amount of outside air will always be supplied by the blower to meet code requirements. If the maximum supply of recirculating air does not raise the room temperature to the desired level, the sensor 23 may also be used to actuate a heating unit of suitable type.

When the outside air reaches a predetermined temperature of say 68 F., an air conditioner may be used to cool the recir culating air, in which event the polarity of the sensor 23 must be reversed so that the damper plate 20 associated wit the recirculating air inlet 14 is opened when the supply temperature goes above a desired temperature level, and the damper plate 19 associated with the outside air inlet 13 is opened when the temperature drops below a certain level. Since there is a net heat gain during the cooling season, the recirculating air damper 20 will ordinarily be substantially fully open except for the stop 42 which permits the minimum ventilating air requirements to be met. Alternatively, sufficient leakage may be permitted around the blower shaft 4 at the outside air inlet 13 to meet minimum ventilating requirements, or other suitable means may be provided for this purpose.

From the foregoing, it can now be seen that the various forms of proportional blowers disclosed herein are capable of blending air or other gases from various sources to supply a desired mixture of constant volume during modulation of one or both blower inlets. When used for ventilating purposes, the blowers permit full modulation up to percent outside air to permit maximum use of natural cooling when available at minimal cost.

We, therefore, particularly point out and distinctly claim as our invention:

1. A proportional blower comprising a blower housing having a pair of spaced inlets and a single outlet, means contained within said blower housing for drawing air or other gases into said inlets and discharging such air through said outlet, movable damper means disposed adjacent each inlet, means interconnecting said damper means for movement toward and away from their respective inlets to increase the effective cross-sectional area of one of said inlets while decreasing the cross-sectional area of the other inlet and vice versa, and restrictor means for reducing the flow through one of said inlets below the flow through the other inlet when both of said damper means are midway between their fully closed and fully open positions so that the combined flow through both of said inlets is substantially the same as the flow through the other inlet when its associated damper means is in the full open position and said one inlet is closed.

2. The proportional blower of claim 1 wherein said restrictor means comprises a fixed restriction at said one inlet.

3. The proportional blower of claim 1 wherein said restrictor means comprises a restrictor plate pivoted to one end of said blower housing in overlying relation to said one inlet, and means interconnecting and restrictor plate to said damper means for pivotal movement of said restrictor plate during movement of said damper means to vary the amount of restriction of said one inlet by said restrictor plate.

4. The proportional blower of claim 3 wherein said interconnecting means causes pivotal movement of said restrictor plate to a nonrestricting position when the damper means associated with said one inlet is in the full open position.

5. The proportional blower of claim 3 wherein said restrictor plate overlies only a portion of said one inlet when in its maximum restricting position, and said means interconnecting said restrictor plate to said damper means permits independent movement of said damper means relative to said restrictor plate during the initial opening and final closing of said one inlet by the associated damper means.

6. The proportional blower of claim 5 wherein said means interconnecting said restrictor plate to said damper means comprises a rod freely slidable in aligned openings in said restrictor plate and associated damper means, and means on the ends of said rod to limit relative movement between said restrictor plate and associated damper means. i

7. The proportional blower of claim 1 further comprising means defining a plenum chamber having communication with said one inlet, and an opening in said plenum chamber through which air is drawn by said blower into said one inlet, said restrictor means comprising a restrictor plate mounted for pivotal movement to restrict the flow through said opening, and linkage means interconnecting said restrictor plate and damper means for causing such pivotal movement of said restrictor plate during movement of said damper means.

8. The proportional blower of claim 1 wherein said restrictor means comprises a restrictor plunger mounted on one of said damper means for movement into and out of said one inlet to restrict the size of said one inlet.

9. The proportional blower of claim 8 wherein said restrictor plunger is of a size less than the size of said one inlet when received therein.

10. The proportional blower of claim 8 further comprising a guide member on said blower housing surrounding a portion of said one inlet, said guide member having an opening therein closely matching a portion of the outer periphery of said restrictor plunger to provide a seal for said restrictor plunger when received therein, whereby said restrictor plunger will restrict said one inlet substantially to the same amount despite variations in the extent of axial overlap between said restrictor plunger and guide member.

it i i 

1. A proportional blower comprising a blower housing having a pair of spaced inlets and a single outlet, means contained within said blower housing for drawing air or other gases into said inlets and discharging such air through said outlet, movable damper means disposed adjacent each inlet, means interconnecting said damper means for movement toward and away from their respective inlets to increase the effective cross-sectional area of one of said inlets while decreasing the cross-sectional area of the other inlet and vice versa, and restrictor means for reducing the flow through one of said inlets below the flow through the other inlet when both of said damper means are midway between their fully closed and fully open positions so that the combined flow through both of said inlets is substantially the same as the flow through the other inlet when its associated damper means is in the full open position and said one inlet is closed.
 2. The proportional blower of claim 1 wherein said restrictor means comprises a fixed restriction at said one inlet.
 3. The proportional blower of claim 1 wherein said restrictor means comprises a restrictor plate pivoted to one end of said blower housing in overlying relation to said one inlet, and means interconnecting and restrictor plate to said damper means for pivotal movement of said restrictor plate during movement of said damper means to vary the amount of restriction of said one inlet by said restrictor plate.
 4. The proportional blower of claim 3 wherein said interconnecting means causes pivotal movement of said restrictor plate to a nonrestricting position when the damper means associated with said one inlet is in the full open position.
 5. The proportional blower of claim 3 wherein said restrictor plate overlies only a portion of said one inlet when in its maximum restricting position, and said means interconnecting said restrictor plate to said damper means permits independent movement of said damper means relative to said restrictor plate during the initial opening and final closing of said one inlet by the associated damper means.
 6. The proportional blower of claim 5 wherein said means interconnecting said restrictor plate to said damper means comprises a rod freely slidable in aligned openings in said restrictor plate and associated damper means, and means on the ends of said rod to limit relative movement between said restrictor plate and associated damper means.
 7. The proportional blower of claim 1 further comprising means defining a plenum chamber having communication with said one inlet, and an opening in said plenum chamber through which air is drawn by said blower into said one inlet, said restrictor means comprising a restrictor plate mounted for pivotal movement to restrict the flow through said opening, and linkage means interconnecting said restrictor plate and damper means for causing such pivotal movement of said restrictor plate during movement of said damper means.
 8. The proportional blower of claim 1 wherein said restrictor means comprises a restrictor plunger mounted on one of Said damper means for movement into and out of said one inlet to restrict the size of said one inlet.
 9. The proportional blower of claim 8 wherein said restrictor plunger is of a size less than the size of said one inlet when received therein.
 10. The proportional blower of claim 8 further comprising a guide member on said blower housing surrounding a portion of said one inlet, said guide member having an opening therein closely matching a portion of the outer periphery of said restrictor plunger to provide a seal for said restrictor plunger when received therein, whereby said restrictor plunger will restrict said one inlet substantially to the same amount despite variations in the extent of axial overlap between said restrictor plunger and guide member. 